1. Field of the Invention
The present invention relates to an objective lens driving device in an optical information recording or reproducing apparatus for a disk-shaped recording medium.
2. Description of Related Art
An objective lens driving device controls and drives an objective lens in two axis directions, namely, the direction perpendicular to a disk-shaped recording medium (referred to as a focusing direction in the following) and the radial direction of the disk-shaped recording medium (referred to as a tracking direction in the following), thereby suppressing a defocusing of the objective lens with respect to an information recording plane of the disk-shaped recording medium (referred to as a disk in the following) and a deviation of an optical axis of the objective lens from a disk track.
In recent years, along with the densification of disk information and the acceleration of disk rotation, it has become necessary to improve the accuracy of the above-described control performance to a higher level. This increases a demand for a wider frequency band and reduced undesired resonance in dynamic characteristics of the objective lens driving device.
On the other hand, it also has become necessary to reduce the size, in particular, the thickness of driving devices. In an optical head including the objective lens driving device, efforts are made to achieve a thinner device by shortening a working distance (referred to as WD in the following) of the objective lens and by reducing a mechanical space between the disk and a lens holder.
However, since the vibration amount of the disk surface is a standard value (for example, the standard for CDs is xc2x10.5 mm), when the objective lens WD is shortened excessively, the objective lens or the lens holder and the disk collide. Accordingly, measures need to be taken with respect to a damage of the disk and the objective lens caused by the collision.
In response to such demands, a protector system against the collision has been suggested in a conventional objective lens driving device, as disclosed in JP 11(1999)-312322 A.
The following is a description of the conventional objective lens driving device (disclosed in JP 11-312322 A), with reference to the accompanying drawing. FIG. 6 is an exploded perspective view showing a configuration of the conventional objective lens driving device.
In FIG. 6, numeral 101 denotes an objective lens, numeral 102 denotes a lens holder, numeral 103 denotes a focusing coil, numerals 104a and 104b denote tracking coils, and numerals 105a and 105b denote coil substrates (the coil substrate 105b is not shown in this figure). The objective lens 101 and the coil substrates 105a and 105b are fixed firmly to the lens holder 102 in their desired position. Furthermore, the focusing coil 103 and the tracking coils 104a and 104b are wound directly around the lens holder 102, and lead terminals of these coils are fixed by soldering to lands of circuit patterns that are formed on the coil substrates 105a and 105b. In the following, a portion constituted by the lens holder 102 and the components described above is referred to as a movable portion.
Numeral 107 denotes a holder substrate, and numeral 109 denotes a suspension holder. As on the coil substrates 105a and 105b, circuit patterns and lands are formed on the holder substrate 107. The suspension holder 109 and the holder substrate 107 are fixed to a back yoke 112b, which will be described below, by a fixing screw 115. Numerals 106a, 106b, 106c and 106d denote metal wire springs (the metal wire spring 106d is not shown in this figure), whose one ends are fixed to the lands on the coil substrates 105a and 105b in the movable portion and the other ends are fixed to the lands on the holder substrate 107 by soldering respectively. They support the movable portion elastically so as to be movable in the focusing direction F and the tracking direction T. A driving current applied to a terminal (not shown in the figure) on the holder substrate 107 is supplied to the focusing coil 103 and the tracking coils 104a and 104b via the metal wire springs 106a to 106d. 
Numeral 112 denotes an actuator base, in which a base portion 112a having a surface parallel to a disk 116 and plate-like back yokes 112b and 112c that are provided in this base portion 112a so as to protrude toward the disk 116 side and to be perpendicular to the disk 116 are formed as one piece. Magnets 113a and 113b are fixed firmly to the back yokes 112b and 112c respectively, with their north poles facing each other. In a magnetic gap of a magnetic circuit formed by the magnets 113a and 113b and the back yokes 112b and 112c, a part of the focusing coil 103 and a part of the tracking coils 104a and 104b are arranged. An electromagnetic force that is generated by a magnetic field in this magnetic gap and the driving current passed through these coils drives the movable portion in the focusing direction F and the tracking direction T. Numeral 114 denotes a shielding yoke for shielding an external magnetic influence.
Numeral 110 denotes a protector, which surrounds the objective lens 101 and is fixed firmly to an upper part of the lens holder 102 by glue 111 so as to protrude furthest from the movable portion toward the disk 116.
The following is a description of an operation of the protector 110. When the movable portion approaches the disk 116 too closely because of a malfunction in the focusing direction F or the like, the protector 110 protruding furthest from the movable portion toward the disk 116 alone collides with the disk 116, thereby preventing the disk 116 and the objective lens 101 from colliding. Also, the protector 110 is formed of a material such as silicone rubber or POM resin, so that the disk 116 is not damaged when colliding.
However, in the conventional objective lens driving device with the above configuration, the protector 110 formed of silicone rubber is fixed firmly to the lens holder 102 by the glue 111. In order to prevent the disk from being damaged, it is indeed appropriate to form the protector 110 with silicone rubber, POM resin or the like, but the silicone rubber and POM resin have an extremely small bonding strength with the glue.
Therefore, there is a problem that the repeated collision causes the protector 110 to come off from the lens holder 102.
Also, the glue has to be applied so as not to be adhered to the colliding surface while fixing the protector 110 firmly. This poses a problem of lowering the working efficiency.
In view of the above-described problems of the conventional objective lens driving device, it is an object of the present invention to provide an objective lens driving device in which a protecting member that is formed of an elastic member such as silicone rubber can be installed without using glue and a damage prevention system that achieves a sufficient holding power even after repeated collisions is provided.
In order to achieve the object mentioned above, the objective lens driving device of the present invention has the following configuration.
A damage prevention system that is provided in the objective lens driving device of the present invention includes a protecting member formed of an elastic member and a fitting portion that is provided in the lens holder and in which the protecting member is inserted while being deformed. Only deforming the protecting member elastically and inserting it in the fitting portion complete the installation of the damage prevention system. Accordingly, it is possible not only to obtain a stable damage-prevention function even without using glue or the like, but also to achieve a protector system that can reduce manufacturing steps considerably.
Also, it is preferable that the protecting member is substantially spherical. This eliminates the need for a consideration of an elastic-deformation direction and an insertion direction when inserting the protecting member in the fitting portion. Thus, it is possible to simplify the assembly. In addition, a stable damage-prevention function always can be obtained regardless of its insertion direction.
Also, it is preferable that the protecting member is formed of an elastic resin.
For example, the protecting member may be formed of a silicone resin. The silicone resin includes rubber-like material such as silicone rubber and resin-like material such as silicone resin in a narrow sense.
Alternatively, the protecting member may be formed of a POM (polyoxymethylene) resin.
In the damage prevention system of the present invention, even when the material of the protecting member is replaced with POM resin or the like, the shape and size of the fitting portion can be set so that the protecting member deforms in an optimal amount according to the material""s elastic modulus. Thus, the material of the protecting member can be selected from a wider range of materials, and a similar effect and result can be obtained with respect to the protecting member made of an arbitrary material.
Also, it is preferable that the fitting portion has a slot shape, with a width smaller than a diameter of the substantially spherical protecting member and a depth greater than a radius of the protecting member. By making the width of the fitting portion smaller than the diameter of the protecting member, the protecting member can be deformed elastically and held. Also, by making the depth of the fitting portion greater than the radius of the protecting member, the contact areas of the protecting member and the internal wall surfaces of the fitting portion can be secured sufficiently. With the above configuration, it is possible to prevent the protecting member from dropping off from the fitting portion.
In addition, it is preferable that a slot serving as the fitting portion has a longitudinal length greater than a length of the protecting member in a direction perpendicular to a compression direction (a diameter), when the length of the protecting member is increased by compressing and deforming the protecting member to have a same width as the fitting portion. With this configuration, the protecting member does not contact the internal wall surfaces of the fitting portion on both ends in the longitudinal direction at the same time when the protecting member is inserted in the fitting portion. Thus, when the protecting member and the disk collide, it is possible to prevent the protecting member from dropping off from the fitting portion because of its impact.
Furthermore, it is preferable that the longitudinal direction of a slot serving as the fitting portion is substantially perpendicular to a rotation direction of the disk. With this configuration, it is possible to obtain a sufficient holding power for opposing an extracting force exerted on the protecting member that is caused by a frictional force or the like between the protecting member and the disk when the protecting member and the disk collide. Also, it is possible to secure a positioning accuracy of the protecting member with respect to the fitting portion.